Finite element analysis using NASTRAN applied to helicopter transmission vibration/noise reduction

A finite element NASTRAN model of the complete forward rotor transmission housing for the Boeing Vertol CH-47 helicopter was developed and applied to reduce transmission vibration/noise at its source. In addition to a description of the model, a technique for vibration/noise prediction and reduction is outlined. Also included are the dynamic response as predicted by NASTRAN, test data, the use of strain energy methods to optimize the housing for minimum vibration/noise, and determination of design modifications which will be manufactured and tested. The techniques presented are not restricted to helicopters but are applicable to any power transmission system. The transmission housing model developed can be used further to evaluate static and dynamic stresses, thermal distortions, deflections and load paths, fail-safety/vulnerability, and composite materials

The geometric paradigm in computational elasto-plasticity

Computational methods, for large displacements of continua in the elastoplastic range, rely on the mathematical modeling of the nonlinear constitutive behavior. In last decades an increasing favor has been deserved to nonlinear models based on a chain decomposition of the deformation gradient. The troubles involved in a structural analysis based on this model are well-known and have not been overcome although many efforts devoted to this end. Our investigation towards a more satisfactory model starts from the new analysis of the rate elastic behavior performed in [1, 2] since the difficulties faced by previous formulations were the very motivation for the discard of rate constitutive models in elasto-plasticity [3]. The new definition of hypo-elasticity, the detection of simple integrability conditions and a new formulation of conservativeness, lead to a definition of rate elasticity suitable for an effective modeling of rate elasto-plastic constitutive behaviors [4]. The treatment is based on a geometric definition of spatial and material fields and on the statement of a geometric paradigm assessing the rules for comparison of material fields naturally provided by push-pull according to the relevant transformation. The rates involved in constitutive relations are Lie-derivatives of stress field and constitutive parameters. Geometric compatibility requires that elastic and plastic stretchings additively give the Lie-derivative of metric field. No privileged reference configuration is involved and no consequent multiplicative decomposition of deformation gradient is assumed. Computational methods are shown to be based on the pull-back of constitutive relations to a straightened out trajectory segment which plays the role of computation chamber wherein linear operations of differentiation and integration may be performed. Accordingly, finite elastic and plastic stretches are considered as purely computational tools with no physical interpretation in constitutive relations. Both 3-D and lower dimensional structural models, such as wires and membranes, may be analysed by a direct application of the theory. The outcome is a significant improvement of physical insight and computational effectiveness with respect to previous treatments of finite elasto-plasticity

Thermal and Structural Analysis of Helicopter Transmission Housings Using NASTRAN

The application of NASTRAN to improve the design of helicopter transmission housings is described. A finite element model of the complete forward rotor transmission housing for the Boeing Vertol CH-47C helicopter was used to study thermal distortion and stress, stress and deflection due to static and dynamic loads, load paths, and design optimization by the control of structural energy distribution. The analytical results are correlated with test data and used to reduce weight and to improve strength, service life, failsafety, and reliability. The techniques presented, although applied herein to helicopter transmissions, are sufficiently general to be applicable to any power transmission system

Analytical Solutions of Viscoelastic Nonlocal Timoshenko Beams

A consistent nonlocal viscoelastic beam model is proposed in this paper. Specifically, a Timoshenko bending problem, where size-and time-dependent effects cannot be neglected, is investigated. In order to inspect scale phenomena, a stress-driven nonlocal formulation is used, whereas to simulate time-dependent effects, fractional linear viscoelasticity is considered. These two approaches are adopted to develop a new Timoshenko bending model. Analytical solutions and application samples of the proposed formulation are presented. Moreover, in order to show influences of viscoelastic and size effects on mechanical response, parametric analyses are provided. The contributed results can be useful for the design and optimization of small-scale devices exhibiting flexural behaviour

On torsion of nonlocal Lam strain gradient FG elastic beams

Abstract The nonlocal strain gradient theory of elasticity is the focus of numerous studies in literature. Eringen's nonlocal integral convolution and Lam's strain gradient model are unified by a variational methodology which leads to well-posed structural problems of technical interest. The proposed nonlocal Lam strain gradient approach is presented for functionally graded (FG) beams under torsion. Static and dynamic responses are shown to be significantly affected by size effects that are assessed in terms of nonlocal and gradient length parameters. Analytical elastic rotations and natural frequencies are established by making recourse to a simple solution procedure which is based on equivalence between integral convolutions and differential equations supplemented with variationally consistent (but non-standard) nonlocal boundary conditions. Effects of Eringen's nonlocal parameter and stretch and rotation gradient parameters on the torsional behavior of FG nano-beams are examined and compared with outcomes in literature. The illustrated methodology is able to efficiently model both stiffening and softening torsional responses of modern composite nano-structures by suitably tuning the small-scale parameters

Strength asymmetries are muscle-specific and metric-dependent

We investigated if dominance affected upper limbs muscle function, and we calculated the level of agreement in asymmetry direction across various muscle-function metrics of two heterologous muscle groups. We recorded elbow flexors and extensors isometric strength of the dominant and non-dominant limb of 55 healthy adults. Participants performed a series of explosive contractions of maximal and submaximal amplitudes to record three metrics of muscle performance: maximal voluntary force (MVF), rate of force development (RFDpeak), and RFD-Scaling Factor (RFD-SF). At the population level, the MVF was the only muscle function that showed a difference between the dominant and non-dominant sides, being on average slightly (3-6%) higher on the non-dominant side. At the individual level, the direction agreement among heterologous muscles was poor for all metrics (Kappa values ≤ 0.15). When considering the homologous muscles, the direction agreement was moderate between MVF and RFDpeak (Kappa = 0.37) and low between MVF and RFD-SF (Kappa = 0.01). The asymmetries are muscle-specific and rarely favour the same side across different muscle-performance metrics. At the individual level, no one side is more performative than the other: each limb is favoured depending on muscle group and performance metric. The present findings can be used by practitioners that want to decrease the asymmetry levels as they should prescribe specific exercise training for each muscle

Invasive Ductular Reaction Operates Hepatobiliary Junctions upon Hepatocellular Injury in Rodents and Humans.

Ductular reaction (DR) is observed in virtually all liver diseases in both humans and rodents. Depending on the injury, DR is confined within the periportal area or invades the parenchyma. On severe hepatocellular injury, invasive DR has been proposed to arise for supplying the liver with new hepatocytes. However, experimental data evidenced that DR contribution to hepatocyte repopulation is at the most modest, unless replicative capacity of hepatocytes is abrogated. Herein, we proposed that invasive DR could contribute to operating hepatobiliary junctions on hepatocellular injury. The choline-deficient ethionine-supplemented mouse model of hepatocellular injury and human liver samples were used to evaluate the hepatobiliary junctional role of the invasive form of DR. Choline-deficient ethionine-supplemented-induced DR expanded as biliary epithelium into the lobule and established new junctions with the canaliculi. By contrast, no new ductular-canalicular junctions were observed in mouse models of biliary obstructive injury exhibiting noninvasive DR. Similarly, in humans, an increased number of hepatobiliary junctions were observed in hepatocellular diseases (viral, drug induced, or metabolic) in which DR invaded the lobule but not in biliary diseases (obstruction or cholangitis) in which DR was contained within the portal mesenchyme. In conclusion, our data in rodents and humans support that invasive DR plays a hepatobiliary junctional role to maintain structural continuity between hepatocytes and ducts in disorders affecting hepatocytes

17.2 Cardiac resynchronization: Multicenter experience with a new coronary sinus lead

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Erectile function recovery after laparoscopic decompression of pudendal artery and nerve: a documented case report

The aim of this article is to report the effectiveness of laparoscopic decompression of pudendal artery (PA) and nerve for erectile dysfunction (ED) restoration. A 32-year-old man consulted for a long-term complaint of ED not responsive to medical therapy. Endocrine screening and neurological evaluation did not show any abnormalities. Color Doppler ultrasound revealed the absence of blood flow in the right PA. After failure of conservative treatments and in accordance to the patient’s desire, laparoscopic pudendal artery decompression was performed. The patient reported significant amelioration of ED one month after surgery. At 8-months follow-up, Doppler ultrasound showed complete revascularization of the right PA